The invention relates to a magnetic tape cassette accommodating case, and more particularly to an improvement of a case for accommodating magnetic tape cassettes, such as audio magnetic tape cassettes, for their storage.
A magnetic tape cassette used for audio, etc., is usually stored in a protecting case when not in use. A magnetic tape cassette has front opening portions into which a magnetic head, etc., is inserted when the cassette is in use in a recording/reproducing apparatus. The cassette stores a magnetic tape therein so that part of the magnetic tape can be traversed along the front opening portions.
The front opening portions of the cassette allow entry of foreign matter such as dust. When dust sticks to the magnetic tape, the recording/reproducing performance may be impaired. Moreover, since the housing of the cassette is molded with a synthetic resin, it may be broken when impacted or dropped. For these reasons, cassettes should be stored in an appropriate case.
A cassette accommodating case consists basically of a cover member having a pocket that receives an end portion of a cassette and a casing member that is pivotably attached to the cover member so as to be opened and closed like a door. The cover member and the casing member are integrally formed with each other using a synthetic resin.
As a synthetic resin for forming the case, polystyrene resin (GPPS) of a common type, which is not only highly transparent but also inexpensive, has often been used. The highly transparent material allows the cassette accommodated in the case and an index card inserted therein together with the cassette to be observed from outside the case.
Although the cassette accommodating case molded with GPPS has the advantage that it is highly transparent, its hardness and surface rigidity are low. For this reason, the pivotably assembled portion and the fitted and held portions are subjected to wear as the case is repetitively opened and closed, and scrapings are produced due to the case being rubbed against the accommodated cassette when storing the cassette or carrying the case. Since the scrapings are a fine powder, they are easily diffused irregularly inside the case, and they tend to adhere to the surface of the magnetic tape exposed at the front opening portions of the cassette. As a result, recording and reproduction cannot be adequately performed on the portion of the tape to which the scrapings have been adhered due to the resulting "dropout" of the reproduction output.
Further, if the case is formed of a highly wear-resistant resin, or a slidable resin, etc., to prevent the production of such scrapings, these resins, generally being low in transparency, do not allow the index card placed inside the case to be observed from outside the case.
A conceivable solution is to selectively use a highly transparent resin and a highly wear-resistant resin. However, in a case that is selectively made of different materials, the respective parts must be molded separately, and the molded parts must be assembled thereafter using an adhesive or the like, making the productivity extremely low.
It has been considered to mold such a case by means of two color molding. However, the molding of the cover member has proved particularly difficult, as will be described with reference to FIG. 6 which is a sectional view showing a mold for molding the cover member.
The injection molding of the cover member 52 (see FIG. 5) will be described with reference to FIG. 6. To mold the cover member 52, a cavity (injection space) is formed between a fixed mold 70 and two movable molds 71, 72 (reference numeral 72 designates a slide core).
After injecting a desired resin into a cavity formed by the respective molds, the resin is appropriately solidified, and the movable molds 71, 72 are moved in directions (directions A and B shown in FIG. 6) so as to release the molds from the fixed mold 70 to form the cover 52. In releasing the molds, the mold 72 must be slid in the direction B so as to pull out its portion located at the inner portion of the pocket to allow the molded product to be released from the molds.
With such an arrangement being a requirement for the molding process, if central portions A (see FIG. 5) of the cover member 52 and its shaded, portions B are to be molded with different resins, another slide core corresponding to the central portions A must also be provided, which slide core must be slidable within the mold 72.
However, since the mold 72 slides in the direction B, it is extremely difficult to drive the other slide core; i.e., moving the mold 72 generally requires that the slide core inside the mold 72 be pulled out from the mold 72 or that coupling between the slide core and the slide core drive device be released. Therefore, even if the slide core is movable, the method for moving the molds as well as the molding process is unavoidably complicated.